[time-nuts] V standards

[Bruce Griffiths]

Poul-Henning Kamp wrote:
> In message <58C70987-017E-44ED-BF07-D578679C03C2 at hughes.net>, Richard Moore wri
> tes:
>
>   
>>> If you are controlling this with a microcontroller, there is an  
>>> alternative
>>> you should consider:
>>>
>>> Use only a single DAC and then PWM modulate its output, followed
>>> by a low-pass filter.
>>>       
>> Poul, how do I PWM a DAC that is itself a PWM device? This question  
>> is prompted by the DAC I'm using in Bert Zauhar's FLL GPSDO, which is  
>> a dithered 10-bit DAC in a PIC chip that results in 14-bit  
>> resolution. I'd like to have a simple way to get 2 to 4 extra bits of  
>> resolution out of this. Can you recommend some design resources to do  
>> this?
>>     
>
> I would simply cummutate the DAC output with a PWM controlled fet or
> CMOS switch.
>
>   
You can either do this with the filtered DAC output and filter the
result, or with some ingenuity just combine the unfiltered PWM outputs
and then filter the result with a single low pass filter.

Bruce